Infinitely adjustable coolant pump

ABSTRACT

A coolant pump for a coolant circuit of an internal combustion engine, the coolant pump having a pump housingin which is mounted a drivable shaft, to one end of which is attached an impeller-which has vanes extending into a suction chamber and is connected to a cover plate. Fluid can be drawn into the suction chamber through an intake port of the pump housing by joint rotation of the impeller and the cover plate and can be conveyed by the vanes into the pump housing. A guide plate, which is axially displaceable by an actuation unit, is disposed between the impeller and the cover plate. The guide plate has a contour corresponding to the impeller and a collar oriented toward the impeller. The coolant pump is characterized in that the guide plate has at least one opening.

The present invention relates to a coolant pump for a coolant circuit ofan internal combustion engine. The coolant pump has a pump housing inwhich is mounted a drivable shaft, to one end of which is attached animpeller which has vanes extending into a suction chamber and isconnected to a cover plate. As a result of the rotation of the coverplate and the vaned impeller, fluid is drawn into the suction chamberthrough an intake port of the pump housing and conveyed further into thepump housing by the vanes. A guide plate, which is axially displaceableby an actuation unit, is disposed between the impeller and the coverplate. The guide plate has a contour corresponding to the impeller and acollar oriented toward the impeller.

BACKGROUND

In order to achieve rapid heating of the internal combustion engine andto selectively adjust the engine temperature, the coolant pump should beswitchable or ideally controllable. This is accomplished selectively byadjusting the flow rate. In order to adjust the flow rate or volumetricflow, the guide plate is axially displaced in the pump within theimpeller. This must be accomplished by an actuator that is preferablyaxially mounted in as neutral a manner as possible in terms of spacerequirements. A coolant pump of the aforementioned type is known fromGerman Patent Application DE 2008 046 424 A1.

SUMMARY OF THE INVENTION

Tests have shown that, depending on the rotational speed, the adjustedposition and the pump design, the resulting hydraulic forces on theguide plate may assume values above 150N. This required amount of forcemust be provided by an actuator which must be capable of adjusting theguide plate at all speeds, temperatures and as frequently as needed.This fact requires an actuating mechanism which is of a certain sizeand/or operates according to a certain basic principle. For this reason,the actuators used are mostly expensive and require a large space.

It is an object of the present invention to provide a switchable orcontrollable coolant pump whose actuator does not require additionalcost or space to provide the forces needed to adjust the guide plate.

The present invention provides that the guide plate has at least oneopening. The opening provided reduces the effective pressure differencebetween the front and rear sides of the guide plate, which in turnreduces the axial force required to displace the guide plate. Fluidcommunication between the front and rear sides of the guide plate isfacilitated. The fluid conveyed radially behind the guide plate has acentrifugal pressure typical of impellers. In conjunction with a certaindynamic pressure component, which is generated when the flow impingesaxially on the rear wall of the impeller after entry through the holes,a mean pressure is generated behind the guide plate. Thus, thepressurized fluid has a force component directed in theguide-plate-closing direction. The guide-plate-closing direction refersto the axial displacement of the guide plate toward the cover plate.This leads to a reduction in the resultant force in theguide-plate-opening direction. The guide-plate-opening direction refersto the axial displacement of the guide plate toward the impeller. Inthis manner, the actuator is relieved of load during the displacementoperation in terms of the force to be exerted.

It has proved advantageous to provide the guide plate with more than oneopening. The openings can have different shapes, such as, for example,flow-optimized shapes in order to make use of flow effects, or radialopenings extending in the guide plate, or shapes which are optimized foreconomical manufacture. Regardless of the specific embodiment, thegreatest effect is achieved when the openings are located in the regionnear the axis of rotation of the guide plate.

Further, the graph of FIG. 4 illustrates the change in the fluid forcesas a function of the degree of opening of the guide plate. Ideally, thefluid force is zero, which would allow the actuator to axially displacethe guide plate without requiring additional force. As can be seen fromthe graph, a fluid force of zero cannot be achieved with a guide platewithout openings. The greater the number of openings, the faster thedecrease in the force level. However, the graph also shows that theforce level becomes negative above a certain degree of opening of theguide plate and a certain number of openings. A negative force level;i.e., negative fluid forces, means that the guide plate moves toward thecover plate, thus preventing the passage of fluid within the water pump,which is to be avoided. In order to enable the actuator to exertsufficient force against the negative fluid forces, it would have to bedesigned stronger and larger, which in turn would result in additionalcosts.

To avoid this, the actuation unit may optionally include a spring. Thisspring applies pressure to the guide plate indirectly via the shaft inthe guide-plate-opening direction. This embodiment provides a fail-safesolution. If the actuator fails and the guide plate is pulled by anegative fluid force in the guide-plate-closing direction, therebyreducing the coolant flow, the spring produces a counterpressure toprevent the guide plate from closing. However, in this embodiment, allof the force curves would have to be increased by the preload of thespring. This would partially cancel out the previously achieved forcereduction.

In order to be able to use a conventional inexpensive actuator, it hasproved advantageous to match the degree of opening of the guide plate tothe number in a suitable this-manner. As a result, a fluid force of20-50 N develops which acts on the guide plate, forcing it toward theimpeller, and thus opening the coolant pump. This is intended to preventnegative fluid forces, which in turn eliminates the need for the use ofa fail-safe spring. In a specific embodiment of the present invention,it is therefore proposed that the impeller have an additional closingcontour pointing in a direction toward the guide plate, and that theclosing contour be engageable into the at least one opening of the guideplate, partially or completely closing the same.

Moreover, provision is made for the closing contour to be configured inthe manner of a pin, the closing contour having more than one pin-likeclosing element, and the individual closing elements differing in theirdimensions (length and/or diameter).

The axially stepped closing contour may be disposed in theinjection-molded portion of the impeller or in the insert thereof. Inaccordance with the present invention, the pins have different lengths,so that when the guide plate is displaced toward the closing contour,first a longer pin-like closing element closes one opening, and when theguide plate is advanced further toward the closing contour, a shorterpin-like closing element closes another opening. It would also bepossible to conceive of closing elements having different diameters andcorresponding openings in the guide plate.

Another option in accordance with the present invention is to configureat least one closing element in a stepped manner, which allows forpartial closure of the opening.

In another preferred embodiment of the present invention, the actuationunit includes an actuator adapted to actuate independently of therotational speed of the impeller.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are shown in FIGS. 1through 4, which are described in detail below, without limiting theinvention to such embodiments.

In the drawing,

FIG. 1 is a cross-sectional view of a controllable coolant pump having aguide plate provided with openings, shown with the guide plate closed;

FIG. 2 a is a schematic view of the guide plate, where its openings areclosed by closing elements;

FIG. 2 b is a schematic view of the guide plate, where only one openingis closed by a closing element;

FIG. 2 c is a schematic view of the guide plate, shown with the openingsopen;

FIG. 3 is a detail view of the guide plate, shown with a stepped closingelement; and

FIG. 4 is a graph showing different fluid force curves as a function ofthe number of openings and the degree of opening of the guide plate.

DETAILED DESCRIPTION

FIG. 1 shows a coolant pump for a coolant circuit of an internalcombustion engine, the coolant pump having a pump housing 1, in which ismounted a drivable shaft 2 a having an impeller 4 attached to one endthereof. Impeller 4 has vanes 6 extending into suction chamber 7.Impeller 4 and cover plate 9 are joined to one another. When impeller 4rotates, fluid is conveyed into suction chamber 7 through an intake port10 of pump housing 1. A guide plate 12, which is axially displaceable byan actuation unit 3, is disposed between impeller 4 and cover plate 9.Guide plate 12 has a contour corresponding to impeller 4 and a collar 13oriented toward impeller 4. In order to achieve rapid heating of theinternal combustion engine and to selectively adjust the enginetemperature, the coolant pump must be controllable or switchable. Tothis end, a volume flow rate is adjusted in accordance with demand. Inorder to adjust the volume flow rate, guide plate 12 is axiallydisplaced in pump housing 1. As guide plate 12 is displaced betweenimpeller 4 and cover plate 9, it changes the degree of opening, therebycontrolling the passage of the flow. Actuation unit 3 includes both theshaft 2 a and a push rod 2 b axially displaceable in shaft 2 a, as wellas an actuator 14 actuating push rod 2 b. Push rod 2 b is directlyconnected to guide plate 12. The displacement of guide plate 12 iscontrolled by actuator 14. Actuator 14 should be incorporated into thecoolant pump in as neutral a manner as possible in terms of spacerequirements. For this reason, the forces resulting from the volume flowand acting on guide plate 12 should be kept as low as possible to beable to choose an actuator 14 that is convenient in terms of space.According to the present invention, to be able to reduce the force levelon guide plate 12, and thus on actuator 14, openings 11 are formed inguide plate 12. The openings 11 formed reduce the effective pressuredifference between the front side of the guide plate (the face facingthe cover plate) and the rear side of the guide plate (the face facingthe impeller). This, in turn, leads to a reduction in the fluid forcesexerted by the fluid flow on guide plate 12. This facilitates the fluidcommunication between the front and rear sides of the guide plate.Further, the radially conveyed fluid forms a pressure cushion on therear side of the guide plate. This pressure results in a force componentin the guide-plate-closing direction, which in turn reduces theresultant force in the guide-plate-opening direction, thereby relievingactuator 14 of load during the displacement operation. Guide plate 12 isclosed when its front side rests against cover plate 9 and flow is nolonger possible. The degree of opening of guide plate 12 is anindication of the amount of flow through the coolant pump. The graph ofFIG. 4 illustrates the relationship between the number of openings 11formed in guide plate 12, the degree of opening of guide plate 12, andthe fluid forces acting on guide plate 12. For a constant degree ofopening of guide plate 12, the force curves decrease as the number ofopenings 11 increases. However, above a certain degree of opening, theforce curves become negative in some regions. This results in a forceacting on guide plate 12 in the guide-plate-closing direction and,therefore, a fail-safe solution is needed. This means that guide plate12 must be prevented from being unintentionally closed as long as theengine needs to be cooled. One way to achieve this would be to use anadditional spring 8. The spring disposed within actuation unit 3 acts onpush rod 2 b. This spring must have a preload such that even if actuator14 fails, guide plate 12 is moved back via push rod 2 b in the directionof impeller 4 to a normal position. In order for these negative forcesto be compensated by a so-called “fail-safe spring”, all of the forcecurves would have to be elevated by the preload of this spring 8. This,in turn, would partially cancel out the force reduction achieved byopenings 11. This would require the use of a powerful actuator 14 whichwould occupy more space.

Therefore, a refinement of the present invention proposes that theopenings 11 of guide plate 12 be variably activated and deactivatedaccording to the degree of opening. This is achieved by a closingcontour 5 formed in the impeller 4 provided with vanes 6. This contourmay be formed in the steel insert of impeller 4 or in theinjection-molded portion thereof, as illustrated in FIGS. 2 through 3.As guide plate 12 is displaced toward impeller 4, pin-like closingelements 5 a engage into one or more openings 11 and close the same. Inthe graph of FIG. 4, an idealized force curve 20 is shown. Idealizedforce curve 20 shows a nearly constant force acting on guide plate 12,regardless of its degree of opening. This idealized force curve 20 canonly be achieved if each time one of the marked operating points S_(x)is reached, a jumps is made to one of the nearest operating points. Thisis achieved by changing the number of openings 11 of guide plate 12 andthe degree of opening of guide plate 12. This is implemented using anaxially stepped closing contour 5 having pin-like closing elements 5 a.Closing elements 5 a engage into openings 11 of guide plate 12 as it isdisplaced between impeller 4 and cover plate 9. The displacement ofguide plate 12 causes a change in the degree of opening. Moreover,because of closing contour 5, different numbers of openings 11 arecleared or closed. FIG. 2 a shows guide plate 12 in an open positionwith the openings closed. This corresponds to an operating range from anopening degree of 100% to operating point S1 in the graph. FIG. 3 showsa stepped, pin-like closing element 5 a, which permits implementation ofhalf-closed openings 11. This corresponds to the operating range betweenoperating points S1 and S2 in the graph. FIG. 2 b shows guide plate 12in a position after having been displaced in the closing direction, andin which one opening 11 is closed. This corresponds to the operatingrange between operating points S2 and S3 in the graph. FIG. 2 c showsguide plate 12 in the closed position in which two openings are open.This corresponds in the graph to the operating range from operatingpoint S3 to operating point S4 or an opening degree of 0%, respectively,depending on the degree of opening.

LIST OF REFERENCE NUMERALS

1 pump housing

2 a shaft

2 b push rod

3 actuation unit

4 impeller

5 closing contour

5 a closing element

6 vane

7 suction chamber

8 spring

9 cover plate

10 intake port

11 opening

12 guide plate

13 collar

14 actuator

20 idealized force curve

S1 operating point 1

S2 operating point 2

S3 operating point 3

S4 operating point 4

1-8. (canceled)
 9. A coolant pump for a coolant circuit of an internalcombustion engine, the coolant pump comprising: a pump housing; adrivable shaft mounted in the pump housing; an impeller attached to oneend of the drivable shaft, the impeller having vanes extending into asuction chamber and being connected to a cover plate, joint rotation ofthe impeller and the cover plate allowing fluid to be drawn into thesuction chamber through an intake port of the pump housing and to beconveyed by the vanes into the pump housing; a guide plate axiallydisplaceable by an actuation unit being disposed between the impellerand the cover plate, the guide plate having a contour corresponding tothe impeller and a collar oriented toward the impeller, the guide platehaving at least one opening.
 10. The coolant pump as recited in claim 9wherein the impeller has a closing contour pointing in a directiontoward the guide plate.
 11. The coolant pump as recited in claim 10wherein the closing contour is engageable into the at least one openingof the guide plate, partially or completely closing the same.
 12. Thecoolant pump as recited in claim 10 wherein the closing contour isconfigured in the manner of a pin.
 13. The coolant pump as recited inclaim 12 wherein the closing contour has more than one pin closingelement, the individual pin closing elements differing in theirdimensions.
 14. The coolant pump as recited in claim 12 wherein theclosing contour includes at least one closing element configured in astepped manner.
 15. The coolant pump as recited in claim 9 wherein theactuation unit includes an actuator adapted to actuate independently ofthe rotational speed of the impeller.
 16. The coolant pump as recited inclaim 9 wherein the actuation unit includes a spring adapted to returnthe guide plate to a normal position.